Oxadiazolopyrimidine derivatives

ABSTRACT

Oxadiazolo[2,3-c]pyrimidine derivatives of the formula ##STR1## wherein R is alkyl, alkenyl, alkynyl or alkoxyalkyl, as well as their salts, are described. The compounds of formula I have valuable, long-lasting vasodilating and/or blood pressure-lowering properties and are useful for the treatment of vascular-conditioned hypertensions or as vasodilators in peripheral blood supply disorders. The compounds are prepared, inter alia, by carbamoylating the corresponding derivative containing a free amino group and optional salt formation.

This is a division of application Ser. No. 327,384, filed Dec. 4, 1981,now U.S. Pat. No. 4,360,521.

BRIEF SUMMARY OF THE INVENTION

The invention relates to oxadiazolo[2,3-c]pyrimidine derivatives of theformula ##STR2## wherein R is alkyl, alkenyl, alkynyl or alkoxyalkyl. aswell as their pharmaceutically acceptable salts.

In another aspect, the invention relates to5-amino-7-[3,6-dihydro-1(2H)-pyridyl]-2H-[1,2,4]-oxadiazolo[2,3-c]pyrimidin-2-oneof the formula ##STR3##

In still another aspect, the invention relates to a process forpreparing the compounds of formula I which comprises reacting5-amino-7-[3,6-dihydro-1(2H)-pyridyl]-2H-[1,2,4]-oxadiazolo[2,3-c]pyrimidin-2-onewith an azole derivative of the formula ##STR4## wherein R is alkyl,alkenyl, alkynyl or alkoxyalkyl and A is --CH═CH--, ##STR5## or --N═CH--whereby the nitrogen is situated in the 2-position.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to oxadiazolopyrimidine derivatives of the formula##STR6## pharmaceutically acceptable salts thereof.

The term "alkyl" as used herein alone or in combination, refers tostraight-chain and branched-chain, saturated hydrocarbon groupscontaining 1-8, preferably 1-4, carbon atoms, for example, methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert.butyl and the like.The term "alkoxy" denotes alkyl ether groups in which the term "alkyl"has the significance set forth above. The term "alkenyl" denotesstraight-chain and branched-chain hydrocarbon groups containing 2-6,preferably 2-3, carbon atoms in which at least one carbon-carbon bond isunsaturated such as allyl, butenyl and the like. The term "alkynyl"denotes straight-chain and branched-chain hydrocarbon groups containing2-6, preferably 2-3, carbon atoms in which at least one carbon-carbontriple bond is present such as propargyl and the like.

Preferred compounds of formula I are those in which R is alkyl oralkenyl. Especially preferred, are those compounds of formula I in whichR is alkyl of 1-4 carbon atoms or alkenyl of 2-3 carbon atoms. Mostespecially preferred are those compounds of formula I in which R isbutyl or allyl, that is, butyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamateand allyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate,respectively.

The compounds of formula I as well as their pharmaceutically acceptablesalts can be prepared in accordance with the invention by

(a) reacting5-amino-7-[3,6-dihydro-1(2H)-pyridyl]-2H-[1,2,4]oxidiazolo[2,3-c]pyrimidin-2-oneof the formula ##STR7## with an azole derivative of the formula ##STR8##wherein R is as previously described and A is one of the groups--CH═CH--, ##STR9## or --N═CH-- whereby the nitrogen atom in the lattercase is situated in the 2-position, and

(b) if desired, converting a compound of formula I obtained into a saltor converting a salt into a pharmaceutically acceptable salt.

The reaction of the compound of formula II with an azole derivative offormula III is carried out according to known methods. Conveniently, theanion of the compound of formula II is reacted with the azole derivativeof formula III. The anion of the compound of formula II isadvantageously prepared in situ by reaction with a base. Bases, forexample, alkali metal hydrides, such as, sodium hydride; alkali metalamides, such as, sodium amide or potassium amide; lithiumdiisopropylamide; potassium t.-butylate and the like, are suitable forthis purpose. The reaction is carried out in a solvent which is inertunder the reaction conditions and at a temperature in the range of fromabout -25° C. to room temperature, preferably in the range of from about0° to 15° C. The solvent can be dimethylformamide, a saturatedhydrocarbon, such as, hexane, an aromatic hydrocarbon, such as, benzene,toluene or xylene, an ether, such as, diethyl ether, dioxane ortetrahydrofuran, and the like.

The starting material of formula II is also an object of the invention.It can be prepared, for example, by cyclizing a compound of the formula##STR10## wherein R is as previously described.

The cyclization of a compound of formula IV is carried out in a knownmanner by heating to a temperature in the range of from about 50° to200°, preferably in the range of from about 100° to 150° C. Thecyclization can be carried out in the absence or presence of a solventor solvent mixture. If the cyclization is carried out in a solvent orsolvent mixture, then the solvent can be an aromatic hydrocarbon such asbenzene, toluene or xylene, an ether such as dibutyl ether, dioxane ordiethyleneglycol dimethyl ether, dimethylformamide and the like ormixtures thereof. It will be appreciated that there can be used either asolvent whose boiling point lies higher than the cyclization temperatureor that there can be used a solvent which boils in the temperature rangereferred to earlier at its reflux temperature. The cyclization ispreferably carried out using dimethylformamide or toluene as thesolvent. The cyclization time depends on the temperature at which thecyclization is carried out and is in the range of from about 1/4 to 18hours. If the cyclization is carried out in the preferred temperaturerange of from about 100° to 150° C., then the cyclization time is in therange of from about 1/4 to 12 hours, preferably 1/4 to 2 hours.

The compounds of formulas III and IV belong to known classes ofcompounds. Accordingly, they are either previously specificallydescribed or can be obtained in analogy to the preparation of the knowncompounds.

The compounds of formula I can be converted into salts, for instance bytreatment with an inorganic base, for example, an alkali hydroxide, suchas sodium hydroxide or potassium hydroxide, or an alkaline earthhydroxide, such as calcium hydroxide. Salts of the compounds of formulaI can also be prepared by double-decomposition of a suitable salt. Ofthe salts of the compounds of formula I, the pharmaceutically usablesalts are preferred.

The compounds of formula I as well as their pharmaceutically acceptablesalts have long-lasting valuable vasodilating and/or bloodpressure-lowering properties and can accordingly be used for thetreatment of vascular-conditioned hypertensions or also as vasodilatorsin the case of peripheral blood supply disorders.

The blood pressure-lowering activity can be determined in conscious,spontaneous hypertensive rats according to the following method:

The systolic blood pressure and the heart rate are measured twice beforeadministration of the test substance. The test substance is administeredby means of an oesophageal probe twice daily, morning and afternoon.Both parameters are measured 1, 3, 6 and 24 hours after theadministration and the percentage variations to the control values arecalculated. The systolic blood pressure is measured indirectly in thetail artery of the rat according to the method of Gerold et al. (Helv.Physiol. Acta 24: 58-69, 1966; Arzneimittelforschung 18: 1285-1287,1968).

The results obtained are compiled in Table I, in each case maximumpercentage deviations from the control values are given. Moreover, thetoxicity values are also given in Table I.

                  TABLE I                                                         ______________________________________                                                           Blood    Heart    Tox. DL.sub.50                                   Dosage     pressure rate     mg · kg..sup.-1                 Compound                                                                              mg · kg.sup.-1                                                                  %        %        p.o.                                     ______________________________________                                        A       30         -14.2    +10.0    >4,000                                           100        -38.4    +13.0                                             B       1          -12.6    +8.2     >5,000                                           3          -33.4    +20.0                                                     10         -40.0    +21.2                                             C       10         -21.8    +12.7    >4,000                                           30         -27.0    +14.3                                             D       10         -31.0    +9.0     >5,000                                   E       1          -24.1    +12.5    >5,000                                           3          -40.9    +9.4                                              F       10         -37.3    +12.7    >5,000                                   G       30         -27.9    +12.2    >5,000                                   H       0.3        -11.3    +17.7    >4,000                                           1          -19.8    +12.8                                                     3          -31.6    -10.1                                                     10         -51.3    -9.1                                              ______________________________________                                         A = Methyl                                                                    7[3,6dihydro-1(2H)--pyridyl2-oxo-2H--[1,2,4]oxadiazolo[2,3c]pyrimidine5-c    rbamate.                                                                       B = Isobutyl                                                                  7[3,6dihydro-1(2H)--pyridyl2-oxo-2H--[1,2,4]oxadiazolo[2,3c]pyrimidine5-c    rbamate.                                                                       C = (2Methoxyethyl)                                                           7[3,6dihydro-1(2H)--pyridyl2-oxo-2H--[1,2,4]oxadiazolo[2,3c]pyrimidine5-c    rbamate.                                                                       D = Butyl 7[3,6dihydro-1(2H)--pyridyl2-oxo-2H--[                              1,2,4]oxadiazolo[2,3c]pyrimidine5-carbamate.                                  E = Propyl                                                                    7[3,6dihydro-1(2H)--pyridyl2-oxo-2H--[1,2,4]oxadiazolo[2,3c]pyrimidine5-c    rbamate.                                                                       F = Isopropyl                                                                 7[3,6dihydro-1(2H)--pyridyl2-oxo-2H--[1,2,4]oxadiazolo[2,3c]pyrimidine5-c    rbamate.                                                                       G = Propargyl                                                                 7[3,6dihydro-1(2H)--pyridyl2-oxo-2H--[1,2,4]oxadiazolo[2,3c]pyrimidine5-c    rbamate.                                                                       H = Allyl                                                                     7[3,6dihydro-1(2H)--pyridyl2-oxo-2H--[1,2,4]oxadiazolo[2,3c]pyrimidine5-c    rbamate.                                                                  

The compounds of formula I and their pharmaceutically acceptable saltscan be used as medicaments, for example, in the form of pharmaceuticalpreparations which contain them in association with a pharmaceuticalorganic or inorganic inert carrier material suitable for enteral orparenteral administration such as, for example, water, gelatine, gumarabic, lactose, starch, magnesium stearate, talc, vegetable oils,polyalkyleneglycols, and the like. The pharmaceutical preparations canbe made up in a solid form, for example, as tablets, dragees,suppositories or capsules, or in a liquid form, for example, assolutions, suspensions or emulsions. If necessary, the pharmaceuticalpreparations can be sterilized and/or can contain adjuvants such aspreserving, stabilizing, wetting or emulsifying agents, salts forvarying the osmotic pressure or buffers. They can also contain stillother therapeutically valuable substances.

The daily dosage in the case of oral administration is in the range offrom about 10 to 500 mg and in the case of intravenous administration isin the range of from about 1 to 50 mg. It will, however, be appreciatedthat these dosages are given by way of example only and can be alteredaccording to the severity of the condition to be treated and accordingto the judgement of the attending practitioner.

The Examples which follow further illustrate the invention. Alltemperatures are given in degrees Centigrade, unless otherwise stated:The melting points are not corrected.

EXAMPLE 1 Preparation of methyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate

4.30 g of sodium hydride (55-60% dispersion in oil) are washed withhexane and suspended in 150 ml of dimethylformamide under argon. 20.54 gof5-amino-7-[3,6-dihydro-1(2H)-pyridyl]-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidin-2-oneare introduced portionwise within 10 minutes into the stirred,ice-cooled suspension, the temperature is held at 14°. The ice-bath isremoved and the mixture is stirred for 30 minutes. Then, a solution of15.8 g of 1-methoxycarbonyl-imidazole in 50 ml of dimethylformamide isadded rapidly and the solution is stirred at 20°-25° for 1 hour. Theclear, red-brown solution is poured into 1.2 l of water, the slightlyturbid solution is filtered through a Speedex filter bed and treatedwith 40 ml of glacial acetic acid while stirring. The precipitate isremoved by filtration and washed thoroughly with 600 ml of water. Thefilter cake is triturated in the suction filter with 400 ml of methanoland the solvent removed by suction. After drying (40°, 20 mm Hg), thereare obtained 23.37 g (91%) of methyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamateas a white powder, m.p. 213° (decomposition).

10.00 g of the crude product are dissolved under reflux in 500 ml ofmethanol and 25 ml of triethylamine and filtered. The warm solution istreated within 30 minutes with 20 ml of glacial acetic acid in 50 ml ofmethanol and the suspension is stirred at room temperature for anadditional 30 minutes. The crystallizate is removed by filtration andwashed thoroughly with three 200 ml portions of methanol. After drying(40°, 20 mm Hg), there are obtained 8.99 g of white crystals, m.p. 215°(decomposition).

The5-amino-7-[3,6-dihydro-1(2H)-pyridyl]-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidin-2-oneused as the starting material can be prepared as follows:

28.8 g of methyl2-amino-6-[3,6-dihydro-1(2H)-pyridyl]-4-pyrimidinecarbamate-3-oxide aretreated with 350 ml of dimethylformamide and the mixture is stirred inan oil-bath at 135° for 30 minutes. The brown solution is evaporatedunder reduced pressure. The still moist residue is suspended in 350 mlof ether for 1 hour and the crystallizate is removed by filtration andwashed with ether. After drying (40°, 20 mm Hg), there are obtained 23.4g (92.5%) of a light beige, crystalline powder, m.p. 228°(decomposition).

The 1-methoxycarbonyl-imidazole used as the starting material can beprepared as follows:

47.2 g of methyl chloroformate in 60 ml of ether are added dropwise at10° within 40 minutes to a stirred solution of 34.05 g of imidazole and52.5 g of triethylamine in 500 ml of acetonitrile. The suspension isstirred at room temperature for 30 minutes. The precipitate is removedby filtration and washed with ether. The filtrate is evaporated underreduced pressure and the residue is taken up in 500 ml of benzene andstirred for 10 minutes. The insoluble material is again removed byfiltration and the filtrate is evaporated under reduced pressure, theresidual oil slowly solidifying. There are obtained 61.7 g (98%) of alight yellowish solid, m.p. 35°-40°, which can be used without furtherpurification.

EXAMPLE 2

In a manner analogous to that described in Example 1, by reacting5-amino-7-[3,6-dihydro-1(2H)-pyridyl]-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidin-2-one

with 1-isobutyloxycarbonyl-imidazole there is obtained isobutyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate,m.p. 197°-198° (from methylene chloride/methanol/diethyl ether),

with 1-(2-methoxyethyl)oxycarbonyl-imidazole there is obtained(2-methoxyethyl)7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate,m.p. 203°-204° (from methylene chloride/methanol/diethyl ether),

with 1-butyloxycarbonyl-imidazole there is obtained butyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]-pyrimidine-5-carbamate,m.p. 197°-198° (from methylene chloride/methanol/diethyl ether),

with 1-ethoxycarbonyl-imidazole there is obtained ethyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxidiazolo[2,3-c]-pyrimidine-5-carbamate,m.p. 202°-204° (from methylene chloride/methanol/diethyl ether),

with 1-propyloxycarbonyl-imidazole there is obtained propyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate,m.p. 201°-202° (from methylene chloride/methanol/diethyl ether),

with 1-isopropyloxycarbonyl-imidazole there is obtained isopropyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate,m.p. 186°-187° (from methylene chloride/methanol/diethyl ether),

with 1-propargyloxycarbonyl-imidazole there is obtained propargyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate,m.p. 211°-213° (from methylene chloride/methanol/diethyl ether) and

with 1-allyloxycarbonyl-imidazole there is obtained allyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate,m.p. 207°-209° (from methylene chloride/methanol/diethyl ether).

The aforementioned imidazole derivatives used as the starting materialsare prepared in a manner analogous to that described in the lastparagraph of Example 1 by reacting imidazole with a correspondingchloroformic acid ester. Since these derivatives are not crystalline atroom temperature, they are characterized with the aid of spectroscopicmethods.

EXAMPLE 3 Preparation of methyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate

1.2 g of sodium hydride are added portionwise to a solution, cooled to15°, of 4.66 g of5-amino-7-[3,6-dihydro-1(2H)-pyridyl]-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidin-2-onein 200 ml of dimethylformamide. The mixture is stirred vigorously atroom temperature for 30 minutes. Thereafter, 5.28 g of1-methoxycarbonylbenzimidazole in 50 ml of dimethylformamide are addedthereto. After 2 hours, the mixture is treated with ice-cold water andadjusted to pH 5 with glacial acetic acid. The precipitate which resultsis recrystallized from methylene chloride/methanol, and there isobtained methyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate,m.p. 212°-214°

The 1-methoxycarbonyl-benzimidazole used as the starting material can beprepared as follows:

16.72 ml of triethylamine are added dropwise to a solution of 11.8 g ofbenzimidazole in acetonitrile. There is added thereto at 10° a solutionof 7.68 ml of methyl chloroformate in 30 ml of ether. The precipitate isremoved by filtration and the solution is evaporated under reducedpressure. The thus-obtained 1-methoxycarbonyl-benzimidazole is usedwithout further purification.

EXAMPLE 4 Preparation of sodium salt of methyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate

13 g of methyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamateare stirred in 100 ml of water and treated slowly with 44.7 ml of 1 Naqueous sodium hydroxide (1.001 mol equivalents), the pH change isfollowed until the pH is stable. As soon as the pH value is stable, thesolution obtained is filtered, freeze-dried and lyophilized. Afterrepeated drying at 50° in a high vacuum, there are obtained 13.5 g ofthe sodium salt of methyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamatein the form of a fine white powder of melting point 192°-198°.

In an analogous manner, from 33 g of butyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxidiazolo[2,3-c]-pyrimidine-5-carbamateand 1.001 mol equivalents of 1 N aqueous sodium hydroxide there isobtained the corresponding sodium salt having a melting point of158°-169°.

EXAMPLE A

Tablets containing the following ingredients are prepared:

    ______________________________________                                        I           Butyl 7-[3,6-dihydro-1(2H)--pyridyl]-                                                                20.0 mg                                                2-oxo-2H--[1,2,4]oxadiazolo[2,3-c]-                                           pyrimidine-5-carbamate (micronized)                                           Lactose (powdered)     40.0 mg                                                Maize starch (white)   24.9                                       II          Dioctyl sodium sulfosuccinate                                                                        0.1  mg                                                Maize starch (white)   5.0  mg                                                Water                  q.s.                                       III  (      Maize starch (white)   6.0  mg                                    IV          Talc                   3.0  mg                                                Magnesium stearate     1.0  mg                                                                       100.0                                                                              mg                                    ______________________________________                                    

The ingredients of group I are sieved and mixed. This mixture ismoistened with the maize starch paste comprising group II and kneaded.The moist mass is granulated, dried and made into a suitable granularsize. Group III is admixed. The resulting mixture is mixed with group IVfor an additional short time. The ready-to-press mixture is pressed intotablets weighing 100 mg, having a diameter of 7 mm and having abreak-bar.

EXAMPLE B

Tablets containing the following ingredients are prepared:

    ______________________________________                                        I           Butyl 7-[3,6-dihydro-1(2H)--pyridyl]-                                                                200.0                                                                              mg                                                2-oxo-2H--[1,2,4]oxadiazolo[2,3-c]-                                           pyrimidine-5-carbamate (micronized)                                           Lactose (powdered)     42.9 mg                                                Maize starch (white)   50.0 mg                                    II          Dioctyl sodium sulfosuccinate                                                                        0.1  mg                                                Maize starch (white)   20.0 mg                                                Water                  q.s.                                       III  (      Maize starch (white)   30.0 mg                                    IV          Talc                   3.5  mg                                                Magnesium stearate     3.5  mg                                                                       350.0                                                                              mg                                    ______________________________________                                    

The ingredients of group I are sieved and mixed. This mixture ismoistened with the maize starch paste comprising group II and kneaded.The moist mass is granulated, dried and made into a suitable granularsize. Group III is admixed. The resulting mixture is mixed with group IVfor an additional short time. The ready-to-press mixture is pressed totablets weighing 350 mg, having a diameter of 11 mm and having abreak-bar.

EXAMPLE C

Capsules containing the following ingredients are prepared:

    ______________________________________                                        I           Butyl 7-[3,6-dihydro-1(2H)--pyridyl]-                                                                20.0 mg                                                2-oxo-2H--[1,2,4]oxadiazolo[2,3-c]-                                           pyrimidine-5-carbamate (micronized)                                           Lactose (powdered)                                                II          Maize starch           5.0  mg                                                Water                  q.s.                                       III         Lactose (crystalline)  50.0 mg                                                Maize starch           15.0 mg                                    IV          Talc                   10.0 mg                                                Magnesium stearate     2.0  mg                                                                       150.0                                                                              mg                                    ______________________________________                                    

The ingredients of group I are sieved and mixed. This mixture ismoistened with the maize starch paste comprising group II and kneaded.The moist mass is granulated, dried and made into a suitable granularsize. Group III is admixed. The resulting mixture is mixed with group IVfor an additional short time. The capsule mixture is filled intocapsules (size 2) each containing 150 mg.

EXAMPLE D

An aqueous drop suspension containing the following ingredients isprepared:

    ______________________________________                                                              10 mg                                                                         per 1 ml                                                ______________________________________                                        Butyl 7-[3,6-dihydro-1(2H)--pyridyl-                                                                  0.1      g                                            2-oxo-2H--[1,2,4]oxadiazolo[2,3-c]-                                           pyrimidine-5-carbamate (micronized)                                           Sodium benzoate         0.035    g                                            Saccharin sodium        0.015    g                                            Acrylic acid polymerizate                                                                             0.1-1.0  g                                            Saccharose              3.5      g                                            Citric acid             0.025    g                                            Polyoxyethylene stearate                                                                              0.002-0.1                                                                              g                                            Sodium hydroxide        q.s.                                                  Flavor                  q.s.                                                  Food coloring           q.s.                                                  Deionized water         ad 10.0  ml                                           ______________________________________                                    

EXAMPLE E

Tablets, capsules and injection preparations can be prepared accordingto the procedures described in Examples A-D using the following,similarly preferred, compounds and their pharmaceutical acceptablesalts:

Methyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate;

ethyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate;

propyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate;

isopropyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate;

isobutyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate;and

allyl7-[3,6-dihydro-1(2H)-pyridyl]-2-oxo-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidine-5-carbamate.

We claim:
 1. The compound5-amino-7-[3,6-dihydro-1(2H)-pyridyl]-2H-[1,2,4]oxadiazolo[2,3-c]pyrimidin-2-oneof the formula ##STR11##